The objective of the present trial was to assess the effect of an EDTA gel applied during surgical periodontal therapy on probing depth reduction and periodontal attachment gain, allowing for the influence on healing of smoking as well as postsurgical oral hygiene. For comparison, citric acid treatment and control surgery only were included. The investigation was performed in one study center involving one clinical investigator and 68 patients. The patients were selected from a consecutive referral material on a voluntary basis. No statistically significant differences between treatment groups concerning attachment gain or pocket depth reduction could be seen after 3 and 6 months. A subgroup of the sample-21 patients who scored zero on the bleeding index at 3 and 6 months postsurgery and did not smoke-had a borderline significantly higher attachment gain in response to experimental treatment as well as a significant pocket depth reduction 6 months postsurgery when controlling for age, gender, Plaque Index at baseline, and treatment in multiple regression analyses. However, this was true not only for EDTA treatment but for citric acid and control treatment as well.